Move the test suite to GitHub Actions

[saadmk11]

This Pull Request moves the test suite to GitHub Actions from travis-ci.

Note:
codecov and travis-ci were not running previously.

[saadmk11]

@safwanrahman Would be great to get your review here.

[saadmk11]

Sample GitHub Action run: https://github.com/saadmk11/django-elasticsearch-dsl/actions/runs/1064789205

[safwanrahman]

Do we really need swap?

[safwanrahman]

I believe 7GB ram would be enough to run the test suite!
https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources

[saadmk11]

This is recommended by elastic:

You must also add the Configure sysctl limits step, otherwise Elasticsearch will not be able to boot.

Ref: https://github.com/elastic/elastic-github-actions/tree/master/elasticsearch#usage

[saadmk11]

@safwanrahman I have removed this and it looks like everything is working as expected, not sure why it was recommended by elastic, maybe there was some edge case before as the README was last updated more than a year ago.

Output: https://github.com/saadmk11/django-elasticsearch-dsl/actions/runs/1119509026

[safwanrahman]

Any particular reason to add it to required ?

[saadmk11]

The test tries to assert VariableLookupError is raised. but VariableLookupError is not raised if required is not True.
This test also fails locally.

django-elasticsearch-dsl/django_elasticsearch_dsl/fields.py

Lines 71 to 75 in 759076b

	if self._required:
	raise VariableLookupError(
	"Failed lookup for key [{}] in "
	"{!r}".format(attr, instance)
	)

[safwanrahman]

Looks very nice! Thanks @saadmk11